High electric resistance for improved magnetic response and improved pulse response to increase pulse frequency are demanded for the magnetic core materials for the recently developed electronic fuel injection systems, solenoid valves, electromagnetic sensors, etc. Further, corrosion resistance to improve environmental adaptability, an excellent cold forgeability and machinability for cost reduction, are also required.
Pure iron, 3Si-iron, 13Cr-2.5Si steel, and 13Cr-1Si-0.25Al steel are currently used for the core materials of the above-mentioned applications.
Pure iron has excellent cold forgeability, however, is poor in electric resistance, magnetic properties and response, and coercive force. 3%Si-iron has an electric resistance of 60.mu..OMEGA..cndot.cm, which is not sufficient, and as the same as in the case of pure iron, is poor in magnetic response and coercive force in addition to corrosion resistance and cold forgeability.
13Cr-2.5Si steel shows excellent electric resistance and corrosion resistance, however, is inferior in magnetic properties, cold forgeability, and machinability. 13Cr-1Si-0.25Al steel excels in corrosion resistance and machinability, but on the other hand, does not have satisfactory electric resistance, magnetic response, coercive force, magnetic flux density, and cold forgeability.
As above mentioned, no currently available steel suffices in all the electric properties (electric resistance), magnetic properties such as magnetic response, coercive force, and magnetic flux density, cold forgeability, machinability, and corrosion resistance.